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   难度：Easy
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   <h1 class="question_title">
    231. Power of Two
   </h1>
   <p>
    Given an integer, write a function to determine if it is a power of two.
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   <p>
    <strong>
     Example 1:
    </strong>
   </p>
   <pre>
<strong>Input:</strong> 1
<strong>Output:</strong> true 
<strong>Explanation: </strong>2<sup>0</sup>&nbsp;= 1
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    <strong>
     Example 2:
    </strong>
   </p>
   <pre>
<strong>Input:</strong> 16
<strong>Output:</strong> true
<strong>Explanation: </strong>2<sup>4</sup>&nbsp;= 16</pre>
   <p>
    <strong>
     Example 3:
    </strong>
   </p>
   <pre>
<strong>Input:</strong> 218
<strong>Output:</strong> false</pre>
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   <h1 class="question_title">
    231. 2的幂
   </h1>
   <p>
    给定一个整数，编写一个函数来判断它是否是 2 的幂次方。
   </p>
   <p>
    <strong>
     示例&nbsp;1:
    </strong>
   </p>
   <pre><strong>输入:</strong> 1
<strong>输出:</strong> true
<strong>解释: </strong>2<sup>0</sup>&nbsp;= 1</pre>
   <p>
    <strong>
     示例 2:
    </strong>
   </p>
   <pre><strong>输入:</strong> 16
<strong>输出:</strong> true
<strong>解释: </strong>2<sup>4</sup>&nbsp;= 16</pre>
   <p>
    <strong>
     示例 3:
    </strong>
   </p>
   <pre><strong>输入:</strong> 218
<strong>输出:</strong> false</pre>
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